1. Technical Field of the Invention
The present invention relates to an electron gun for microwave tubes such as traveling-wave tube (TWT) and Klystron.
2. Description of the Prior Art
Microwave tubes are used mainly as microwave amplifiers at earth stations and relay stations for microwave satellite communication. Recently, the microwave tubes are required to be small and light, as the earth stations and relay stations becomes compact and light in weight. Particularly, compact size and light in weight of the TWT for a repeater which is mounted in the satellite is of great importance.
A conventional hot cathode electron gun disclosed in JP 09115453 A, 1997 is shown in FIG. 4. As shown in FIG. 4, hot cathode 102 is joined with stepped metal cylinder 118 which is joined with another stepped metal cylinder 117 which is further joined with focus electrode cylinder 119. Cathode 111, anode 113, heater electrode 122 are insulated form one another by insulating cylinders 112 and 112xe2x80x2, while cathode 111 is connected with focus electrode cylinder 119 and anode 113 is connected with a metal member consisted of metal cylinder 114 and anode electrode plate 115. Further, one end 120 of a heater lead wire is connected with heater electrode 120, while the other end 121 if the same is connected with metal cylinder 117. The electron gun as explained above is sealed be sealing metal 123 and is connected with a not-shown RF frequency circuit by sealing plate 116. Here, anode 113 is insulated from the not-shown RF circuit by using insulating cylinder 112xe2x80x3.
Further, a conventional cold cathode electron gun also disclosed in the above-mentioned JP 09115453 A, 1997 is shown in FIG. 5. As shown in FIG. 5, cold cathode 1 is joined with metal member 2 through plate 21a. Further, metal member 2 goes through insulating cylinder 3 which is joined with stepped metal cylinder 9 which mounts focus electrode 8. Here, metal cylinder 9 is connected with a not-shown gate of cold cathode 1 by conductive wire 10, while insulating cylinder 3 is joined with insulating cylinder 4. Further, the not-shown gate is connected electrically with gate metal cylinder 7 by metallized layer 31c. Here, metallized layers 31a and 31b are used for obtaining electric connection at the connecting portion, respectively. The electron gun as explained above is contained in metal cylinder 5. Further, metal cylinder 5 and insulating cylinder 4 are joined with stepped metal cylinder 6.
However, the surrounding of the above-mentioned conventional hot electron guns must be furthermore insulated, because the insulating cylinders are stacked for the insulation of each electrode and high voltages are applied directly to the surrounding of the electron gun. Accordingly, insulating material must be fixed by using a jig of which diameter is greater than the surrounding.
On the contrary, it is not necessary to fix the insulating material around the external surrounding of the above-mentioned conventional cold cathode electron gun, because the surrounding is grounded electrically and each electrode is extracted along the axis of the electron gun. However, the above-mentioned conventional cold cathode electron gun has a disadvantage that its outer radius becomes great, due to the additional metal cylinder for obtaining electrical ground. Therefore, electron gun can not be made small and light.
Further, the structures of the above-mentioned hot and cold electron gun are so complex that it is difficult to manufacture them.
Therefore, an object of the present invention is to provide an electron gun, wherein its structure is simple and further electrodes can be extracted along its axis.
The hot cathode electron gun of the present invention comprises first stepped metal cylinder 201 which is joined with cathode 200, second metal cylinder 202 which is joined with first stepped metal cylinder 201, metal plate 221 which is joined with second metal cylinder 202, insulating cylinder 220 which is joined with metal plate 221, third metal cylinder 260 which is joined with the outer surface of insulating cylinder 220, fourth metal cylinder 210 which is joined with third metal cylinder 260, stepped insulating cylinder 250 which is joined with fourth stepped metal cylinder 210, and fifth metal cylinder 270 which is joined with stepped insulating cylinder 250.
In this electron gun, fifth metal cylinder 270 is grounded electrically. Further, cathode lead wire, anode lead wire, heater lead wire are extracted along the axis of the gun.
In place of the hot cathode, a cold cathode is also applicable, and cathode lead wire, anode lead wire, and gate lead wire are extracted along the axis of the gun.
In the electron gun of the present invention, an insulating cylinder is used as a vacuum envelope, and the electrodes are extracted along the gun axis.
According to the present invention, it is not necessary to insulate the surrounding of electron gun, because an insulating cylinder is used as a vacuum envelope and the electrodes are extracted along the axis of the electron gun. Therefore, the electron gun can be made small and light.
Further, the insulating cylinder as a vacuum envelope operates also as a jig for filling up insulating material around the high voltage terminals of the electrodes, because the terminals are positioned inside the insulating cylinder. Therefore, conventional jigs become needless. Accordingly, manufacturing processes of the electron gun are simplified.